An absorbent article, such as a pants-type disposable diaper, includes: a front waistline portion to be fitted to the front waist of a wearer; a back waistline portion to be fitted to the back waist of the wearer; and a crotch portion to be fitted to the crotch of the wearer. Here, leg-surrounding regions into which the legs of the wearer are inserted are formed at both sides of the crotch portion.
The front waistline portion and the back waistline portion are joined to each other in a region extending from an edge portion of a waist opening to be fit around the body of the wearer to each leg-surrounding region. Japanese Patent Application Publication No. Hei 5-15551 discloses a technique of joining a web in predetermined regions thereof, where joint portions of the front waistline portion and the back waistline portion are to be formed, by causing a joining apparatus to apply ultrasonic vibration to the predetermined regions (for example, see PTL 1).
In general, the joining apparatus includes: an ultrasonic vibrating device applying ultrasonic vibration to the predetermined regions of continua of diaper components under conveyance; an anvil roller including protrusions for pressing the continua in the predetermined regions between the anvil roller and the ultrasonic vibrating device; a motor rotating the anvil roller; and a belt (connector) connecting the anvil roller and the motor.
In the joining apparatus with the aforementioned configuration, the driving of the motor in association with the conveyance of the continua rotates the anvil roller via the belt. Then, an ultrasonic horn provided in the ultrasonic vibrating device and one of the protrusions of the anvil roller work together to nip the continua in each predetermined region at a certain interval (i.e., the interval corresponding to a distance between each adjacent predetermined regions). Thereby, the continua in the predetermined region are subjected to ultrasonic vibration and joined.
The inventors have discovered that, in the known joining apparatus mentioned above, while the motor keeps driving the belt to rotate the anvil roller, the rotational speed of the anvil roller is reduced temporarily when the ultrasonic horn of the ultrasonic vibrating device comes in contact with each protrusion of the anvil roller. This induces a problem of loosening the belt between the motor and the anvil roller, and thus causing the belt to run off the anvil roller or the motor.
Moreover, the rotational speed of the anvil roller is changed drastically when the ultrasonic horn comes in contact with the protrusion. This results in a non-uniform joining in the predetermined regions, that is, a non-uniform joining in the joint portions of the front waistline portion and the back waistline portion.
It is desirable to provide a joining apparatus and a method of manufacturing absorbent articles which are capable of achieving a more uniform joining in predetermined regions thereof, where joint portions of a front waistline portion and a back waistline portion are to be formed, and of reliably preventing a connector such as a belt from running off an anvil roller or a motor, in a case where the anvil roller and the motor are connected to each other via the connector.